Resistive elements are used in a wide range of applications. One such application relates to signal-conditioning and/or filtering. Signal-conditioning and filtering applications often use resistive elements as part of a signal-conditioning circuit. The responses of the signal-conditioning circuits depend upon the resistive values of the resistive elements. Thus, the signal-conditioning circuits are designed with resistive elements having values that are tailored towards the specific applications.
The true resistive value for resistive elements varies according to specific manufacturing parameters, which can lead to resistive mismatches for a signal-conditioning circuit with tight design parameters. The resistive value can also vary according to temperature, which can adversely affect the signaling-conditioning circuit. Moreover, devices are continuing to be used in applications that require tighter constraints on the signal-conditioning circuits. Further complicating the issue, some devices use a variety of different signals, which can each require a different set of signal-conditioning parameters. Coupled with increasing demand for smaller, faster, cheaper, and less power-hungry devices, a standard/static resistive element is often inadequate.
Accordingly, various circuits use resistors with adjustable resistances. The use of adjustable resistors allows for both wider ranges of applications, for fine tuning of the actual resistive value and for feedback circuits that control the resistive value.
A particular type of an adjustable resistor is implemented using CMOS transistors as the resistive element. Important aspects of such adjustable resistor can include the linearity of the resistance and range of adjustable resistive values.